Efficient and Adhesiveless Metallization of Flexible Polyimide by Functional Grafting of Carboxylic Acid Groups

Abstract

Surface metallization of polyimide (PI) is the key process for the preparation of flexible printed circuit boards (FPCBs). To meet the miniaturization demand, the ultrathinness of FPCB by the removal of the intermediate adhesive layer is imperative. The common adhesiveless process relies on the surface activation of hydrophobic PI through alkaline hydrolysis to generate the hydrophilic carboxylate anion sites for the metallic deposition. However, the alkaline hydrolysis process involves the imide ring cleavage caused by the attack of a strong nucleophile (OH − ), resulting in mechanical destruction and surface coarseness of PI. In this study, a new PI is synthesized with the grafting of carboxylic acid groups as the active sites to intrinsically activate PI for efficient metallization. The surface activation is accomplished through an acid−base neutralization reaction in a dilute alkaline environment, which can suppress the alkaline hydrolysis reaction. The attenuated total reflection Fourier transform infrared spectroscopy analysis confirms a significant reduction of the extent of the imide ring cleavage in the carboxylic acid-grafted PI films. According to the microstructural examination using transmission electron microscopy, the deposited metal film adheres firmly to the carboxylic acid-grafted PI films through an interlocking effect of a broccoli bud-shaped nanocluster layer.

A Sub‐Square‐Millimeter Microbattery with Milliampere‐Hour‐Level Footprint Capacity

“…[ 17 ] Although the nucleophilic attack does not apply to the aqueous ZnSO 4 electrolyte (2 mol L –1 ), CO bonding of PI (Figure S5, Supporting Information) form potential attacking sites for the nucleophilic oxygen. [ 18 ] X‐ray photoelectron spectroscopy (XPS) is used to investigate the interfacial composition of electrodes. In addition to the CO bonding at 531.5 eV ( Figure 3 a, upper panel), O–(CO) bonding at 533 eV in the O 1s spectrum of MnO 2 ‐PI is observed, indicating the nucleophilic attack of the CO bonding and the formation of an electrode–electrolyte interface.…”

Challenges, Prospects, and Emerging Applications of Inkjet‐Printed Electronics: A Chemist's Point of View

“…Liu et al. recently presented a Kapton containing carboxylic acid functions that allow the deployment of extremely rich and robust surface chemistry [201] …”

Sandwich-Layered Dielectric Film with Intrinsically Excellent Adhesion, Low Dielectric Constant, and Ultralow Dielectric Loss for a High-Frequency Flexible Printed Circuit

“…Nevertheless, it is still a great challenge to balance the paradox between superior dielectric property and excellent adhesion. , As a thermosetting polyolefin resin, 1,2-polybutadiene (1,2-PB) has shown great potential as a matrix resin in the fields of electronics, insulations, adhesives, coatings, automobile tires, , and toughening modifiers . Attributed to the low electronic polarizability of C–C and C–H bonds in polyolefins, 1,2-PB exhibits low dielectric constant and ultralow dielectric loss over wide frequency and temperature ranges. , Unfortunately, unmodified nonvulcanized polybutadiene (PB) also suffers from inherent drawbacks such as poor interfacial adhesive strength between the resin and copper foil and easy creeping, which make it hard to adhere with other substances (e.g., copper foil) and to laminate them.…”

“…Nevertheless, it is still a great challenge to balance the paradox between superior dielectric property and excellent adhesion. 21,22 As a thermosetting polyolefin resin, 1,2polybutadiene (1,2-PB) has shown great potential as a matrix resin in the fields of electronics, 23 insulations, 24 adhesives, coatings, automobile tires, 25,26 and toughening modifiers. 27 Attributed to the low electronic polarizability of C−C and C− H bonds in polyolefins, 1,2-PB exhibits low dielectric constant and ultralow dielectric loss over wide frequency and temperature ranges.…”